Inducing apoptosis in macrophages

[J.S. Good]

How can I induce apoptotic cell death over 24-72h in J774 macrophages,
rather than simply adding a cytotoxic agent which kills them all stone
dead
immediately? I want to test some other substances for cytotoxicity, and
would like to establish a scale on which they might fall.

Thanks for any advice.

James